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Fix an infinite loop where a transform in InstCombiner::visitAnd claims a construct is changed when it is not. (See included testcase.)

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Patch by Xiaoyi Guo.



git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@140072 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Eli Friedman 2011-09-19 21:58:15 +00:00
parent 1494c496e2
commit c6b8ba8673
2 changed files with 29 additions and 21 deletions
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43
lib/Transforms/InstCombine/InstCombineAndOrXor.cpp
View File

@ -1174,30 +1174,31 @@ Instruction *InstCombiner::visitAnd(BinaryOperator &I) {
((A == C && B == D) || (A == D && B == C)))
return BinaryOperator::CreateXor(A, B);
if (Op0->hasOneUse() &&
match(Op0, m_Xor(m_Value(A), m_Value(B)))) {
if (A == Op1) { // (A^B)&A -> A&(A^B)
I.swapOperands(); // Simplify below
std::swap(Op0, Op1);
} else if (B == Op1) { // (A^B)&B -> B&(B^A)
cast<BinaryOperator>(Op0)->swapOperands();
I.swapOperands(); // Simplify below
std::swap(Op0, Op1);
// A&(A^B) => A & ~B
{
Value *tmpOp0 = Op0;
Value *tmpOp1 = Op1;
if (Op0->hasOneUse() &&
match(Op0, m_Xor(m_Value(A), m_Value(B)))) {
if (A == Op1 || B == Op1 ) {
tmpOp1 = Op0;
tmpOp0 = Op1;
// Simplify below
}
}
}
if (Op1->hasOneUse() &&
match(Op1, m_Xor(m_Value(A), m_Value(B)))) {
if (B == Op0) { // B&(A^B) -> B&(B^A)
cast<BinaryOperator>(Op1)->swapOperands();
std::swap(A, B);
if (tmpOp1->hasOneUse() &&
match(tmpOp1, m_Xor(m_Value(A), m_Value(B)))) {
if (B == tmpOp0) {
std::swap(A, B);
}
// Notice that the patten (A&(~B)) is actually (A&(-1^B)), so if
// A is originally -1 (or a vector of -1 and undefs), then we enter
// an endless loop. By checking that A is non-constant we ensure that
// we will never get to the loop.
if (A == tmpOp0 && !isa<Constant>(A)) // A&(A^B) -> A & ~B
return BinaryOperator::CreateAnd(A, Builder->CreateNot(B, "tmp"));
}
// Notice that the patten (A&(~B)) is actually (A&(-1^B)), so if
// A is originally -1 (or a vector of -1 and undefs), then we enter
// an endless loop. By checking that A is non-constant we ensure that
// we will never get to the loop.
if (A == Op0 && !isa<Constant>(A)) // A&(A^B) -> A & ~B
return BinaryOperator::CreateAnd(A, Builder->CreateNot(B, "tmp"));
}
// (A&((~A)|B)) -> A&B

7
test/Transforms/InstCombine/and2.ll
View File

@ -35,3 +35,10 @@ define i1 @test4(i32 %X) {
; CHECK: @test4
; CHECK-NEXT: ret i1 false
}
; Make sure we don't go into an infinite loop with this test
define <4 x i32> @test5(<4 x i32> %A) {
%1 = xor <4 x i32> %A, <i32 1, i32 2, i32 3, i32 4>
%2 = and <4 x i32> <i32 1, i32 2, i32 3, i32 4>, %1
ret <4 x i32> %2
}